The present invention relates to a process for producing polymer-shell nanoparticles, especially in the form of aqueous dispersions, and to the production of suspoemulsions which are converted to the aqueous dispersions of the nanoparticles.
The controlled formation and structuring of polymer-shell nanoparticles, especially of nanoparticles with core-shell structure, is of particular interest in order to achieve particular properties of the nanoparticles for highly specialized uses. Coated nanoparticles are of interest for numerous applications, for example as pigments in colorant compositions or as catalysts. The polymer coating prevents the agglomeration of the particles, which leads to a higher color intensity or an improved catalyst performance. In the medical field of application, marker substances are polymer-coated in order to suppress damaging effects of the particles on the organism. In addition, the polymer coating of the particles can serve for protection from external influences on the particles, for example corrosion, oxidation, reduction, water inter alia. It is also possible to modify properties, for example the conductivity of coated particles. One possibility here is, for instance, coated nanoparticles as hybrid materials for printed electronics, consisting of semiconductive or conductive polymers with semiconductive or conductive inorganic particles. This gives rise to a broad field of use for nanoparticles with core-shell structure in optical, electronic, chemical, biotechnological and medical systems.
For production of the polymer-shell nanoparticles, emulsion polymerization processes are frequently used, since these allow the formation of structured nanoparticles, for instance with a core-sheath or core-shell structure.
Lee et al., J. Eur. Ceram. Soc. 1999, 19, 15, 2593-2603, describe the synthesis of spherical ZrO2 microparticles, wherein two inverse microemulsions comprising precursor substances or reactants in the aqueous disperse phase are mixed and reacted.
K. Landfester, Adv. Mater. 2001, 13, 10, 765-768, describes the production of miniemulsions and the use of miniemulsions in the synthesis of nanoparticles and encapsulated nanoparticles.
WO 2008/058958 describes the production of core-shell particles, wherein an outer layer is applied to solid nanoparticles dispersed in a mini-suspoemulsion, by converting a precursor substance dissolved in the disperse phase in an emulsion process with an emulsion in the disperse phase and thus applying it to the dispersed nanoparticles.
WO 2008/116839 describes a process for high-pressure dispersion of reactive monomers for production of nanoparticle-laden monomer emulsions.
WO 2010/133465 describes a process for producing nanoparticles or nanostructured particles with the aid of a two-emulsion method, wherein particles are produced by controlled coalescence of miniemulsions in a high-pressure homogenizer.
N. Nabih et al., J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 23, 5019-5029, describe the synthesis of inorganic polymer hybrid particles which are produced by a multistep miniemulsion process. However, the process is found to be laborious and not very suitable for a continuous configuration, since the miniemulsions are produced by treatment of conventional emulsions by means of an ultrasound homogenizer, which is unsatisfactory in terms of time consumption and energy expenditure and cannot be incorporated into a continuous process regime.
The processes described in the prior art for production of polymer-shell nanoparticles have the disadvantage that intermediate stabilization of the nanoparticles obtained in an intermediate step is necessary, for example by means of surfactant addition. Moreover, the prior art does not disclose any process for producing polymer-shell nanoparticles using emulsions or suspoemulsions, which can be configured as an integrated continuous process.
It is an object of the invention to provide a process for producing polymer-shell nanoparticles, especially in the form of nanoparticles with core-shell structure which can especially be configured in an economically viable manner as a continuous integrated process, without the need for intermediate stabilization of the nanoparticles.